Antenna



United States Patent Phillip H. Smith, Newark, N. J., assignor to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York Application April 28, 1951, Serial No. 223,490 28 Claims. (Cl.250-33. 63)

This invention relates to. radio transmission and, more particularly todirective, antennas.

The principal object of the invention is to improve the radiationpattern of a directive microwave antenna of the type. comprising anarray of horns. Other objects are to simplify the construction andreduce the cost of such antennas.

One type of directive antenna for radiating into space or interceptingmicrowaves comprises a linear array of tapered electromagnetic hornsconnected to a hollow-pipe wave guide with a longitudinal spacingapproximately equal to an integral number of wavelengths within theguide at the operating frequency. The minimum spacing of the horns isthus one wavelength within the guide. However, since a wavelength isshorter in free space than in the guide, the spacing of the horns attheir mouths will be greater than a wavelength in free space.

In an array of the type described, undersired secondary radiation lobesappear on each side of the main lobe. I have found, however, that theseundesired lobes may be greatly reduced or substantially eliminated bydecreasing the spacing of the horns at their mouths, preferably to lessthan a wavelength in free space. But it is apparent that the hornscannot be spaced closer, because they would no longer be fed within-phase energy.

In accordance with the present invention this difficulty is overcome bysubdividing each horn into a plurality of similar horns by means of oneor more partitions in its magnetic plane. If only one partition is used,it is centrally positioned in the horn and extends inwardly from theplane of the horn mouth. In the preferred embodiment the partition atfirst gradually increases in thickness from its outer end, at such arate as to divide the original horn into two horns whose longitudinalaxes are parallel, and then gradually decreases in thickness to a linein the magnetic plane, to minimize reflections. In order to provide adistribution of energy among the original horns which will give thegreatest directivity, the feed guide is preferably tapered in theelectric plane. This desired energy distribution may be maintainedbetween the two horns formed by each partition by locating the inner endof the partition somewhat to one side of' the center line of theoriginal horn. To provide the best over-all impedance characteristic forthe divided horn, the flaring portion and the tapering portion of thepartition each preferably have an axial length approximately equal to anintegral number of half wavelengths in free space at the operatingfrequency.

The nature of the invention will be more fully understood from thefollowing detailed description and by reference to the accompanyingdrawings, of which Fig. 1 is a perspective view of a portion of anantenna array embodying the invention; and

Fig. 2 is a sectional side elevation of the antenna structure shown inFig. 1

The figures show an end portion only of an antenna array, constitutingone embodiment of the invention, comprising a hollow-pipe wave guide 3to which are connected ice a plurality of tapered electromagnetic horns4, 5, and 6 arranged in line, with their mouths in the same plane 8. Thehorns may be made of any suitable conducting ma terial, The completeantenna array may, for example, be a balanced structure of the generaltype shown in Fig. 13 of United States Patent No. 2,405,242, granted toG. C. Southworth on August 6, 1946.

As indicated by the double-pointed arrow 9, the elec tromagnetic wavesof the operating frequency f are either supplied to or withdrawn fromthe guide 3 at the left end. In the description which follows it will beassumed that the antenna is operating as a radiator. The guide 3 isrectangular in cross section and the electric field of the energytherein is perpendicular to its wider sides, as indicated by the arrowE1 in Fig. 12. In the horns 4, 5, and 6 the electric field has thedirection indicated by the arrow E2. In order to improve the directivityof the array, the guide 3 is preferably tapered in the electric plane sothat the horns receive less and less energy as their distance from thesource increases. Therefore, as shown, the E-plane dimension is shorterat the right end than at the left; end of the guide The horns 4, 5, and6, are connected to the guide 3 through the apertures 10, 11, and 12respectively, which extend transversely across one of the wider sidesthereof and have a uniform longitudinal spacing A approximately equal toan integral number of wavelengths hg within the guide 3 at the frequencyf. Each of the horns 4, 5, and 6 is provided at its throat with a scoop14 which extends across the guide 3 in the magnetic plane thereof andserves to divert the proper amount of energy into the associated horn.It is to be noted that, with this tapered construction of the guide 3,the scoops 14 are all identical, thus simplifying the, construction. Thescoops 14. are held in place by means. of the pins 15 which pass throughholes in the. narrower sides of the guide 3 and fit into holes 16 in thescoop.

The horns 4, 5, and 6 are secured to the guide 3 by means of the bars 17which extend transversely across the top of the guide and are. fastened.thereto by the screws 19. The horn is secured at its throat to the sideof the bar 11 as, for example, by soldering, pinning or otherwise.Adjacent horns are separated at their mouths by the spacers 20 and theassembly is held together by means of two rods 21 which pass throughholes near the ends of the spacers 20 and are secured by the pins 22.The horn array may be fastened to an appropriate supporting structure,not shown, by means of brackets such as 24 attached to the end spacer20. by a screw 25.

A horizontal horn array of the type thus far described may be designedto radiate a horizontally polarized beam which is quite sharplydirective. As a typical example, a balanced array of 18 horns has beenbuilt in which the major lobe is 2.75 degrees wide in azimuth angle, at3 decibels below the peak intensity, when the operating frequency f is8815 megacycles per second. There were also present, however, twoundesired minor lobes, each 3 /2 degrees in width, located at 41 degreeson either side of the axis of the array. Investigation showed that thisextraneous wide-angle radiation was caused largely by the fact that thespacing B of the horns at their mouths was too great. The spacing B,although equal to A is equal to approximately 1.5x, where A is awavelength in free space. It was found that the undesired wide-anglelobes could be substantially eliminated if the spacing B could bedecreased to x or less. However, the horns 4, 5, and 6' cannot be spacedcloser because the spacing A of the apertures 10, 11, and 12 already hasits minimum permissible value of hg. If A and B are further reduced, thehorns will not be fed with in-phase energy from the guide 3.

In accordance withthe present invention this, difiiculty is overcome byinserting into each horn a partition 26 in the magnetic plane, thus ineffect doubling the number of horns in the array and thereby reducingtheir spacing to B/ 2, which is only 0.7 Sr. These partitions may bemade of metal, or of other suitable material covered or coated withmetal or metal foil, preferably of good conductivity, and soldered orotherwise secured in place. For best results the partitions must be ofspecial shape, determined largely by the shape of the original horn. Itis necessary that the two horns, such as 5' and 5" into which the horn 5is divided, shall have their longitudinal axes parallel to each other aswell as to the longitudinal axis of the original horn. To accomplishthis, the partition 26 is centrally positioned in the horn 5 and extendsinwardly from the plane 8 for a distance C throughout which it graduallyincreases in thickness at such a rate as to divide the horn 5 into twoidentical horns 5 and 5" whose longitudinal axes are parallel. Statedanother way, the surfaces of the partition 26 are gradually flaredinwardly at the same (but oppositely inclined) angle as that of thecorresponding wall of the original horn 5. Similar partitions 26 arealso inserted in the same manner into the horn 4 to form the horns 4,4", and into the horn 6. In order that all of the identical horns thusformed shall have a uniform spacing B/Z between their longitudinal axes,the width D of the partition 26 at the top is made equal to the width Gof the spacer 20. To minimize reflections, the partition 26 is taperedthroughout its lower portion H substantially to a line, or knife edge,30 in the magnetic plane. In order to improve the overall impedancecharacteristic of the horn assembly, the axial length of each of theportions C and H of the partition 26 is made approximately equal to anintegral number of half wavelengths in free space at the frequency f. Inorder to preserve the desired amplitude taper at the throat of thehorns, such as 4', 4'", the inner end 30 of the partition 26 may bedisplaced somewhat from the center of the original horn 4, in thedirection away from the source of energy. Thus, in the horn 4 thedistance I from the end 30 to the left wall is greater than the distanceK to the right wall.

When the partitions 26 were added to the 18-horn array mentioned above,the two unwanted wide-angle radiation lobes were substantiallyeliminated without materially affecting the major central lobe.

As a further extension of the invention, each of the original horns maybe divided into four or more substantially identical horns. As shown inFig. 2, the horn 6 may first be divided into two identical horns by thepartition 26. Then, a partition 31, similar to the partitions 26, may becentrally positioned in the magnetic plane of each of these two horns toform four substantially identical horns 33, 34, 35, and 36 havingparallel axes. In like manner the horns 4, 4", 5', and 5" may besubdivided by additional partitions 31, not shown. With this baffiearrangement the spacing A between the apertures 10, 11, 12 can be madeequal to 2)\g and still the spacing L of the horns 33, 34, 35, 36 willbe only 0.75%, which is sufficiently close in many cases.

What is claimed is:

1. A radio antenna comprising a hollow-pipe wave guide having in oneside thereof a plurality of apertures with a longitudinal spacingapproximately equal to an integral number of wave-lengths within saidguide at the operating frequency, a corresponding number of taperedelectromagnetic horns of rectangular cross section connected at theirthroats to said guide respectively at said apertures, each of said hornsincluding a longitudinal partition extending into said horn, the outerend of said partition lying in the plane of the mouth of said horn anddividing said horn into two equal rectangles and said partition at firstincreasing in thickness from the outer end thereof at such a rate as todivide the original horn into two substantially identical rectangularhorns whose longitudinal axes are substantially parallel and thengradually decreasing in thickness substantially to a line.

2. An antenna in accordance with claim 1 in which the thickness of saidpartition at its outer end is substantially equal to the distance at themouth between the inner surface of the wall of one of said originalhorns and the inner surface of the wall of an adjacent original horn.

3. An antenna in accordance with claim 2 in which said partitionincreases in thickness from the outer end thereof for an axial distanceequal to an integral number of half wavelengths in free space at saidoperating frequency.

4. An antenna in accordance with claim 3 in which said partitiondecreases in thickness from its widest point for an axial distance equalto an integral number of half Wavelengths in free space at saidoperating frequency.

5. An antenna in accordance with claim 4 in which the inner end of saidpartition is nearer to one Wall of the original horn than to theopposite wall thereof.

6. An antenna in accordance with claim 1 in which said partitionincreases in thickness from the outer end thereof for an axial distanceequal to an integral number of half wavelengths in free space at saidoperating frequency.

7. An antenna in accordance with claim 6 in which said partitiondecreases in thickness from its widest point for an axial distance equalto an integral number of half wavelengths in free space at saidoperating frequency.

8. An antenna in accordance with claim 1 in which said partitiondecreases in thickness from its widest point for an axial distance equalto an integral number of half wavelengths in free space at saidoperating frequency.

9. An antenna in accordance with claim 1 in which all of said identicalhorns have substantially uniform spacing between their longitudinalaxes.

10. An antenna in accordance with claim 1 in which said guide isrectangular in cross section with unequal cross-sectional dimensions,and said apertures are in one of the wider sides of said guide.

11. An antenna in accordance with claim said horns are of the samelength.

12. An antenna in accordance with claim 1 in which the mouths of saidhorns are adjacently arrayed in line in the same plane.

13. A radio antenna comprising a rectangular hollowpipe wave guide withunequal cross-sectional dimensions having in a wider side thereof aplurality of apertures with a longitudinal spacing approximately equalto an integral number of wavelengths within said guide at the operatingfrequency, a corresponding number of tapered rectangular electromagnetichorns each having a rectangular throat with unequal cross-sectionaldimensions and a rectangular month, each of said horns being connectedat its throat to said guide at one of said apertures with the largercross-sectional dimension of said throat parallel to the largercross-sectional dimension of said guide, each of said horns including alonigtudinal partition with maior faces parallel to the largercross-sectional dimension of the throat of the horn, the outer end ofsaid partition dividing the mouth of the horn into two equal rectangles,said partition at first increasing in thickness for an axial distance Cfrom the outer end thereof at such a rate as to divide the original horninto two substantially identical horns Whose longitudinal axes aresubstantially parallel and then gradually decreasing in thickness for anaxial distance H.

14. An antenna in accordance with claim 13 in which said original hornsare of equal length.

15. An antenna in accordance with claim 13 in which the inner end ofsaid partition is substantially a line.

16. An antenna in accordance with claim 13 in which said distance C isequal to an integral number of half wavelengths in free space at saidoperating frequency.

17. An antenna in accordance with claim 13 in which said distance H isequal to an integral number of half wavelengths in free space at saidoperating frequency.

18. An antenna in accordance with claim 13 in which 1 in which thethickness of said partition at its outer end is equal to the distance atthe month between the inner surface of the wall of one of said originalhorns and the inner surface of the wall of an adjacent original horn.

19. A radio antenna comprising a plurality of similar taperedrectangular electromagnetic horns having rectangular mouths adjacentlyarrayed in line in the same plane and having a common longitudinalcenter plane, means for feeding into each of said horns electromagneticwaves of the same phase to establish therein electric fields in adirection parallel to said common center plane, each of said hornsincluding a longitudinal partition with major faces perpendicular tosaid common center plane, the outer end of said partition dividing themouth of the horn into two equal rectangles, and said partition at firstincreasing in thickness from the outer end thereof at such a rate as todivide the original horn into two substantially identical horns whoselongitudinal axes are substantially parallel and then graduallydecreasing in thickness.

20. A tapered electromagnetic horn of rectangular cross section havingunequal cross-sectional dimensions at the throat and a longitudinalpartition within said horn, said partition having its major facesparallel with the larger cross-sectional dimension of said throat, theouter end of said partition dividing the mouth of said horn into twoequal rectangles, said partition at first increasing in thickness fromthe outer end thereof at such a rate as to divide said horn into twosubstantially identical horns whose longitudinal axes are substantiallyparallel and then gradually decreasing in thickness, and the inner endof said partition being nearer to one wall of the original horn than tothe opposite wall thereof.

21. A horn in accordance with claim 20 in which said partition decreasesin thickness substantially to a line.

22. A tapered electromagnetic horn of rectangular cross section and alongitudinal partition within said horn, the outer end of said partitiondividing the mouth of said horn into two equal rectangles, saidpartition increasing in thickness from the outer end thereof at such arate as to divide said horn into two substantially identical horns whoselongitudinal axes are substantially parallel and then graduallydecreasing in thickness, and the inner end of said partition beingnearer to one wall of the original horn than to the opposite wallthereof.

23. A radio antenna comprising a hollow-pipe wave guide having in oneside thereof a plurality of apertures with a longitudinal spacingapproximately equal to an integral number of wavelengths within saidguide at the operating frequency, a corresponding number of taperedelectromagnetic horns of rectangular cross section connected at theirthroats to said guide respectively at said apertures, each of said hornsincluding a longitudinal partition extending into said horn, the outerend of said partition lying in the plane of the mouth of said horn anddividing said mouth into two equal rectangles, said partition at firstincreasing in thckness from the outer end thereof at such a rate as todivide the original born into two substantially identical rectangularhorns whose longitudinal axes are substantially parallel and thengradually decreasing in thickness substantially to a line, the thicknessof said partition at its outer end being substantially equal to thedistance at the mouth between the inner surface of the wall of one ofsaid original horns and the inner surface of the wall of an adjacentoriginal horn, and the inner end of said partition being nearer to onewall of the original horn than to the opposite wall thereof.

24. A radio antenna comprising a hollow-pipe wave guide having in oneside thereof a plurality of apertures with a longitudinal spacingapproximately equal to an integral number of wavelengths within saidguide at the operating frequency, a corresponding number of taperedelectromagnetic horns of rectangular cross section connected-at theirthroats to said guide respectively at said apertures, each of said hornsincluding a longitudinal partition extending into said horn, the outerend of said partition lying in the plane of the mouth of said horn anddividing said mouth into two equal rectangles, said partition at firstincreasing in thickness from the outer end thereof at such a rate as todivide the original horn into two substantially identical rectangularhorns whose longitudinal axes are substantially parallel and thengradually decreasing in thickness substantially to a line, and the innerend of said partition being nearer to one wall of the original horn thanto the opposite wall thereof.

25. A radio antenna comprising a hollow-pipe Wave guide having in oneside thereof a plurality of apertures with a longitudinal spacingapproximately equal to an integral number of wavelengths within saidguide at the operating frequency, a corresponding number of taperedelectromagnetic horns of rectangular cross section connected at theirthroats to said guide respectively at said apertures, each of said hornsincluding a longitudinal partition extending into said horn, the outerend of said partition lying in the plane of the mouth of said horn anddividing said mouth into two equal rectangles, said partition at firstincreasing in thickness from the outer end thereof at such a rate as todivide the original horn into two substantially identical rectangularhorns whose longitudinal axes are substantially parallel and thengradually decreasing in thickness substantially to a line, and saidguide being rectangular in cross section with unequal cross-sectionaldimensions and tapering in the smaller cross-sectional dimension.

26. An antenna in accordance with claim 25 in which the inner end ofsaid partition is nearer to one wall of the original horn than to theopposite wall thereof.

27. An antenna in accordance with claim 13 in which the inner end ofsaid partition is nearer to one wall of the original horn than to theopposite wall thereof.

28. An antenna in accordance with claim 19 in which the inner end ofsaid partition is nearer to one Wall of the original horn than to theopposite wall thereof.

References Cited in the file of this patent UNITED STATES PATENTS2,405,242 Southworth Aug. 6, 1946 2,425,488 Peterson et al Aug. 12, 19472,461,005 Southworth Feb. 8, 1949 2,477,633 Litton Aug. 2, 19492,480,829 Barrow Sept. 6, 1949 2,530,079 Riblet Nov. 14, 1950 2,628,311Lindenblad Feb. 10, 1953

